The present invention relates to an electrophotographic photoconductor and to a method of manufacturing the substrate for the electrophotographic photoconductor.
Electrophotographic techniques, developed at first for copying machines, are now applied also to laser printers, since electrophotographic techniques facilitate printing with higher printing quality, at higher printing speed and with less audible noise than by conventional impact printing techniques.
FIG. 4 is a partial cross-sectional view of a conventional electrophotographic photoconductor. Referring now to FIG. 4, the electrophotographic photoconductor includes a cylindrical tubular substrate 1 made of aluminum or other such conductive material. A machined surface 1a is formed on the substrate 1 by cutting, grinding, polishing or other such surface machining technique. An undercoating layer 2, that includes an anodized oxide film or an organic resin film, is formed on the machined surface 1a. A photoconductive layer 3 is formed on the undercoating layer 2 by laminating a charge generation layer 3a and a charge transport layer 3b, which include photoconductive materials. The undercoating layer 2, the charge generation layer 3a, and the charge transport layer 3b, each including an organic resin film, are formed through a series of dip-coating processes.
Pure aluminum or aluminum alloy tubing has been mainly used for the substrate. In addition, various surface machining and treatment techniques and various finishing techniques, including provision for an undercoating layer, have been proposed for the substrate. The proposed techniques include cutting with a turning tool, grinding with an abrasive tape or an abrasive wheel, buffing, honing, and chemical polishing. (See Japanese Unexamined Laid Open Patent Applications No. S59-74567, No. S60-112049, No. S61-42663, No. S62-186270, No. H01-316752, No. H04-269760, and No. H04-300163.)
Recently, aluminum tubing (or porthole tubing), the surface of which has not been finished by cutting, has been widely used due to the recent technological development in the tubing manufacture and due to the rationalization of the surface finishing of the tubing. The specified surface state and dimensional precision of this tubing can be attained by drawing or by ironing the tubing manufactured by extrusion. However, small flaws or pits may be caused in the photoconductive layer of the photoconductor by the stripes, specific to the porthole tubing, along the cylindrical axis of the tubing. In addition, residual surface stress caused by drawing remains. Further, the degree of oxidation and wettability of the tubing surface exhibit wide distributions. In addition, it is difficult to remove the highly viscous oil used in the drawing process. These defects of the substrate surface make it difficult to obtain a photoconductive layer with uniform film quality and thickness. The surface defects of the substrate also cause uneven color in the external appearance of the photoconductor and uneven printing density in the image quality.
The cost of the substrate occupies a very large portion of the manufacturing costs of a high-quality photoconductor, which includes a photoconductive layer with a uniform film thickness and quality. The substrate is costly because it is necessary to apply a variety of finishing processes to the substrate surface, such as preliminary cutting, polishing and, depending on the structure of the photoconductive layer, forming of an anodized oxide film on the substrate surface.
Recently, the finishing processes of the substrate have been further individualized and complicated as varieties of substrate material and tubing have been used. Tiny irregularities in a finishing process causes nonuniformity in the film thickness and film quality of the photoconductive layer. The nonuniformity in the film thickness and film quality of the photoconductive layer causes an unfavorable external appearance of the photoconductor such as uneven color and luster; unwanted image defects such as black spots, voids and uneven printing density; and unfavorable electrical performances such as irregular charge retention and poor repeatability.
Accordingly, there exists a need to provide a simplified method of manufacturing a substrate for an electrophotographic photoconductor at a low cost.